The present invention relates to a process for the preparation of pure high quality 3,3xe2x80x2, 4,4xe2x80x2-tetraminobiphenyl (TAB) of formula 1 in high yields. 
3,3xe2x80x2,4,4xe2x80x2-Tetraminobiphenyl (TAB) is a valuable intermediate and final product in various areas. For example, TAB is used as monomer in the preparation of polybenzimidazole (PBI) polymers, which are characterized by excellent thermal and mechanical stability. These PBI polymers are widely used as proton-conducting materials for fuel cell applications (compare U.S. Pat. Nos. 2,895,948, 3,174,947, 5,317,078 and 6,187,231). TAB is also used as an antioxidant and as an agent for stabilizing epoxide resins.
In the prior art, TAB has been prepared by three known methods. One such known method is ammonolysis of 3,3xe2x80x2-dichlorobenzidine (DCB) in the presence of mainly Cu catalysts, including both copper salts and elemental Cu, using aqueous NH3. For example, French Patent Specification No. 1,475,631 describes such an ammonolysis of DCB, in the presence of a CuI salt and/or of Cu2O and CaCl2, at an elevated temperature, preferably 150-210xc2x0 C. and under an elevated inert gas pressure. The crude TAB thus obtained is purified via its salt formation with a strong acid. The yield of TAB is about 70%. Subsequently, various attempts have been made to obtain TAB in highly pure form and in high yields from crude TAB as described below.
U.S. Pat. No. 3,865,876 describes an improvement on the result of the method described in French Patent Specification No. 1,475,631 by using essentially only CuCl as a catalyst for the ammonolysis of DCB. The yield of TAB of theory having purity of about 75-82% is between about 85 and 87%. This product has a Cu content of about 3-6% by weight.
U.S. Pat. No. 3,943,175 discloses the use of CuCl and Cu powder as a catalyst. It also describes the purification of TAB by using of sulfuric acid, converting it to sulfate, isolation of the sulfate and liberation therefrom of TAB by means of a base. The TAB thus liberated is dissolved and reprecipitated from an aqueous solution advantageously with the addition of activated charcoal and diatomaceous earth. However, the Cu content present in TAB is about 0.6 to 0.9% and the yield at most 45.7% of theory, relative to DCB employed.
German Patent DE 3,111,470 discloses the purification of crude TAB obtained by ammonolysis process by boiling it with H2O containing activated carbon and sodium dithionate. The yield of TAB using the disclosed process is 75.9% with xe2x89xa60.0005% Cu content.
Japanese Patent No. 60,158,146 also describes the purification of TAB by refluxing the crude TAB with activated charcoal, aqueous FeCl3 solution and hydrazide hydrate. The yield of TAB using the disclosed process is 83.2% containing xe2x89xa710 ppm Cu.
The purification of crude TAB obtained from ammonolysis of DCB with copper catalyst by crystallizing it in water in presence of 0-5% by weight of activated carbon and about 1-2% by weight of a water-soluble reducing agent, i.e. alkali metal dithionate or alkali metal sulfite, at temperature of 100-140xc2x0 C. under N2 atmosphere has been disclosed. (U.S. Pat. Nos. 4,433,168, 5,235,105 and Eur. Pat. Appl. EP 522,577). The yield of TAB using the disclosed process is 88.2% of theory with only 10 ppm Cu).
In a second method for producing TAB, which has generated substantial interest, the starting material is benzidine which is acetylated with acetic anhydride, to form N,N-diacetylbenzidine. The latter compound is then nitrated with conc. HNO3 to form 3,3xe2x80x2-dinitro-N, N-diacetylbenzidine which is base hydrolyzed to form 3.3xe2x80x2-dinitrobenzidine. This is then reduced by any of various means to form TAB (H. Vogel and C. S. Marvel, J. Poly. Sci. Part Al, 1531 (1963)).
In a third method for the production of TAB, biphenyl is used as the starting material. The method comprises the following six steps: (1) acetylating the biphenyl in the presence of an appropriate Friedelxe2x80x94Crafts catalyst to obtain 4,4xe2x80x2-diacetylbiphenyl (DAcB); (2) oximating the DAcB to form DAcB dioxime; (3) subjecting the dioxime to a double Beckmann rearrangement to obtain N,Nxe2x80x2-diacetylbenzidine (DiAcBz); (4) nitrating the DiAcBz to obtain 3,3xe2x80x2-dinitro-N,Nxe2x80x2-diacetylbenzidine (DNAcBz); (5) removing the acetyl groups of the DNAcBz by basic hydrolysis to form 3,3xe2x80x2-dinitrobenzidine (DNB) and (6) reducing the nitro groups of DNB to form TAB (U.S. Pat. No. 5,041,666).
There are various disadvantages associated with the foregoing methods. The use of benzidine, for example, as one of the raw materials, is undesired since it is a known carcinogen.
Direct ammonolysis of DCB catalyzed by copper salts also requires high temperatures (200xc2x0-300xc2x0 C.) at a pressure of 900-1000 psig, which causes the manufacturing process to be hazardous. The use of such harsh reaction conditions is undesired.
Direct ammonolysis of DCB as disclosed by the prior art methods generates tarry materials, which always accompany the TAB produced.
Direct ammonolysis also causes the formation of stable complexes, where copper is likely complexed with TAB in situ, requiring the extraction of TAB from the complex. Furthermore, direct ammonolysis also causes the formation of other stable complexes, where copper is likely complexed with the corresponding triaminobiphenyl. This impurity must also be removed during the manufacturing process.
Lastly, the prior art methods utilize relatively expensive starting materials. Thus, any method for producing TAB utilizing a cheaper raw material, which is both safer and easier to handle, would be very desirable.
The main object of the present invention is to provide an improved process for the preparation of pure high quality 3,3,xe2x80x24,4xe2x80x2-tetramino biphenyl (TAB), which avoids the drawbacks as discussed above.
Another object of the present invention is to provide for the use of heterogeneous Ti-superoxide as a catalyst for the oxidation of DCB to obtain 3,3xe2x80x2-dichloro-4,4xe2x80x2-dinitrobiphenyl (DCDNB). DCDNB which smoothly underwent ammonolysis affording 3,3xe2x80x2-dichloro-4, 4xe2x80x2dinitrobiphenyl (DADNB), followed by the reduction of nitro groups of DADNB yielded TAB in high yields.
Yet another object is to provide a novel process for the synthesis of TAB of greater purity than then achieved using the methods disclosed by the prior art.
The present invention relates to a process for the preparation of pure high quality 3,3xe2x80x2, 4,4xe2x80x2-tetraminobiphenyl (TAB) in high yields.
More particularly, it relates to a process for preparation of 3,3xe2x80x2,4,4xe2x80x2 tetraminobiphenyl (TAB) involving a three step process comprising (1) oxidation of 3,3xe2x80x2-dichloro 4,4xe2x80x2-diaminobiphenyl (DCB) with 50% aqueous H2O2, (2) ammonolysis of the resulting 3,3xe2x80x2-dinitro 4,4xe2x80x2-dinitrobiphenyl (DCDNB) and (3) the reduction of 3,3xe2x80x2-diamino-4,4xe2x80x2-dinitrobiphenyl (DADNB) with stannous chloride and concentrated hydrochloric acid.